1. Field of the Invention
The present invention relates to a system for cooling a vehicle battery.
2. Background Art
There are a variety of vehicles today which utilize electricity, and in particular an electric motor, to at least assist in powering the vehicle. For example, there are electric vehicles, which are powered exclusively by an electric motor; hybrid electric vehicles (HEV), which may be selectively powered by an internal combustion engine or an electric motor; and fuel cell vehicles, or hybrid fuel cell vehicles, just to name a few. The electric motor used in such vehicles may have an electrical power source such as a fuel cell or a battery.
In the case of a battery used to provide power to an electric motor to drive a vehicle, the temperature of the battery can increase significantly when the motor is used for extended periods of time. The increase in battery temperature may be compounded when the battery is confined to a relatively small, enclosed space. If the increase in battery temperature is left unchecked, the battery life may be reduced. Thus, it is desirable to provide a system for cooling a battery, or batteries, in a vehicle to keep the battery temperature low enough that the battery life is not reduced.
One attempt to provide cooling to a battery in an electric automobile is described in U.S. Pat. No. 5,490,572 issued to Tajiri et al. on Feb. 13, 1996. Tajiri et al. describes a system for cooling a number of batteries in a battery chamber. Air from outside the vehicle may be taken directly into the battery chamber, or the air may first pass through a heat exchanger to cool it before it flows into the battery chamber. Some of the air that flows through the heat exchanger may flow into a vehicle passenger compartment, rather than into the battery chamber.
Thus, in the system described in Tajiri et al., the same heat exchanger is used to cool both passenger compartment air and battery compartment air. A number of air discharge ports may be opened or closed to control the flow of air into the passenger compartment; however, the temperature of the air flowing into the passenger compartment will be the same as the temperature of the air flowing into the battery compartment. This is because a single heat exchanger is used to cool the air flowing into both spaces. The air that flows into the battery chamber is discharged outside the vehicle, while the air flowing into the passenger compartment may be discharged outside the vehicle, or recirculated back into the passenger compartment.
One limitation of the system described in Tajiri et al. is the lack of separate controls for the air flowing into the passenger compartment and the battery compartment. For example, if the temperature of the batteries increases such that the system attempts to provide cool air to the battery compartment, and the temperature of the air outside the vehicle is not low enough to adequately cool the batteries, a damper will be closed to force air through the heat exchanger for cooling, prior to flowing into the battery chamber. If at the same time, the vehicle occupants request warm air into the passenger compartment, a conflict arises, because there is a single heat exchanger used for both the passenger compartment air and the battery compartment air.
Another limitation of the system described in Tajiri et al. is the inability to recirculate air within the battery chamber. For example, when the batteries need to be cooled, but the vehicle occupants do not wish to receive air cooled by the heat exchanger, air discharge ports leading into the passenger compartment can be closed. Air cooled by the heat exchanger then passes into the battery compartment; however, there is no mechanism for recirculating the air back through the battery compartment. Instead, it is discharged to the ambient environment outside the vehicle. This may be inefficient, since the cooled air passing through the battery compartment may still be at a lower temperature than the ambient air outside the vehicle. In such a situation, it would be beneficial to recirculate the air from the battery compartment back through the heat exchanger where it could be more efficiently cooled than the outside ambient air. Moreover, recirculating the air may provide the added benefit of reducing the moisture content of the air passing through the heat exchanger. This could reduce the amount of condensate formed and help prevent icing of the heat exchanger.
Another system for cooling a battery in a vehicle is described in U.S. Pat. No. 5,937,664 issued to Matsuno et al. on Aug. 17, 1999. Matsuno et al. describes a system for cooling a battery, wherein batteries inside a battery chamber are cooled by air taken from the vehicle passenger compartment. After passing through the battery compartment, the air may be recirculated into the passenger compartment, or discharged through an exhaust duct. One limitation of the system described in Matsuno et al. is its reliance on air from the vehicle passenger compartment to cool the batteries. Because the vehicle occupants determine the passenger compartment temperature based on their own comfort level, the air in the passenger compartment may be too warm to adequately cool the batteries. Just as in the system described in Tajiri et al., such a situation presents a conflict between the comfort level of the vehicle occupants and the need to cool the batteries.
Thus, a need still exists for a system for cooling a vehicle battery that does not rely on passenger compartment air, but rather, can alternatively provide air to cool the batteries taken directly from ambient air outside the vehicle, or air passed through a heat exchanger separate from a heat exchanger used to cool the passenger compartment air. Moreover, there is also a need for a system for cooling a battery that provides for recirculation of the air from the battery compartment and back through a heat exchanger so as to cool the air more efficiently, and thereby provide an energy savings.